Photoelectrode material and photocell material

ABSTRACT

A method of generating electricity utilizing silicon oxide is provided. The method includes irradiating a light to a photocell comprising a photovoltaic material which consists essentially of silicon oxide in a manner that causes the silicon oxide to generate the electricity in response to the irradiation of light, and correcting the electricity from the photovoltaic material.

CROSS-REFERENCE OF RELATED APPLICATIONS

This application is a Continuation application Ser. No. 13/503,558,filed May 22, 2012, which is a 371 of International Application No.PCT/JP2010/068548, filed Oct. 21, 2010, which claims priority ofJapanese Patent Application No. 2009-242432, filed Oct. 21, 2009,Japanese Patent Application No. 2010-088571, filed Apr. 7, 2010,Japanese Patent Application No. 2010-206914, filed Sep. 15, 2010Japanese Patent Application No. 2010-229129, filed Oct. 8, 2010, theentire contents of which are incorporated herein by reference.

FIELD OF INVENTION

The present invention relates to a photocell or a photoelectrodeutilizing silicon dioxide as a photovoltaic material to generate anelectric power and an electric power generation method utilizing thesame.

BACKGROUND ART

Generally, with respect to a reaction which cannot proceed without veryhigh energy, for advancing such a reaction with extremely low energy,there is used a photocatalyst which causes an electron excitation stateby irradiation with light. As photocatalysts, there have been knownso-called semiconductor catalysts, such as titanium oxide, zinc oxide,cadmium sulfide, and tungstic oxide, and metal complex catalysts, suchas a ruthenium bipyridyl complex.

Among these photocatalysts, titanium oxide (TiO₂) is the most stable andsubstantially not biologically poisonous, and therefore is practicallyused as the photocatalyst for decomposing and removing nitrogen oxidesand organic substances in air. However, for titanium oxide only theultraviolet light having a wavelength of 380 nm or less can be used. Theultraviolet light in this region of wavelength is as small as 4% of thesunlight, and therefore titanium oxide achieves only the utilizationefficiency for sunlight, which is the most abundant light source, 4% atthe most, and practically at the most 1% thereof.

Typical examples of photocatalytic reactions of titanium oxide includereduction of O₂ (formation of H₂O₂), oxidation of H₂O (generation ofO₂), reduction of methylbiologen, reduction of N₂, drainage treatment,and a photocatalytic Kolbe reaction {CH₃COOH→CH₄ (gas)+CO₂}.

Titanium oxide has a photocatalytic ability as well as a photoelectrodeability to electrolyze water, which is known as a Honda-Fujishimaeffect, and a photovoltaic ability used in a solar cell.

JP-A-2004-290748 (Japanese Patent No. 4214221) and JP-A-2004-290747(Japanese Patent No. 4247780) show fused quartz treated with a halogenacid as a material having a photocatalytic ability similar to that oftitanium oxide.

International Publication No. WO2005/089941 shows synthetic quartztreated with hydrofluoric acid as a material having a photocatalyticability.

This photocatalyst functions as a photocatalyst in a wavelength regionof 200 to 800 nm, which is wider than the wavelength region for thephotocatalyst using the fused quartz shown in JP-A-2004-290748 andJP-A-2004-290747.

With respect to the synthetic quartz treated with hydrofluoric acid,International Publication No. WO2005/089941 has descriptions therefor atparagraphs [0021] to [0023] of the publication.

The synthetic quartz is activated by the treatment with hydrogenfluoride as mentioned above is explained as follows. When SiO₂ and HFare in contact with each other, Si on the surface is bonded to F, sothat the bonded electrons are drawn toward the F side and the back bondis weakened. As a result, this site is attacked by the separated H⁺F⁻molecules, and the back bond is cleaved, so that Si on the uppermostsurface is fluorinated, and simultaneously one of the bonds in the layerimmediately below the surface is hydrogenated.

The above state is successively transmitted, and Si on the uppermostsurface is finally separated in the form of SiF₄, so that SiH₃ radicalsremain on the surface.

In the SiH₃ radicals, however, the Si—Si bond between Si in the radicaland Si in the next layer is very weak, and further the bonded electronsare weakly drawn toward the H side, and therefore the Si—Si bond iseasily cleaved, so that Si is easily replaced by H in the HF moleculesto give a form of SiH. Therefore, H is exposed on the Si (111) surface,thus causing an activated state.

The synthetic quartz treated with hydrogen fluoride is separated fromthe solution, and washed with distilled water 2 to 5 times, followed byair drying, to obtain the photocatalyst.

The synthetic quartz is activated by hydrogen fluoride as mentionedabove, but natural quartz, which comprises the same crystalline silica,is not activated by hydrogen fluoride. The reason for this has not yetbeen elucidated.

International Publication No. WO2006/095916 shows zinc oxide, tindioxide, tungsten oxide, and silicon carbide as semiconductorphotoelectrode materials other than titanium dioxide used in theultraviolet region.

Further, there are shown silicon, gallium arsenide, strontium titanate,cadmium selenide, and gallium phosphide as semiconductor photoelectrodematerials used in the visible light region.

BACKGROUND ART REFERENCES

Document 1: JP-A-2004-290748

Document 2: JP-A-2004-290747

Document 3: International Publication No. WO2005/089941

Document 4: International Publication No. WO2006/095916

SUMMARY OF THE INVENTION

For the photoelectrode and the solar cell each using titanium oxide,only the ultraviolet light having a wavelength of 380 nm or less, whichis contained as small as 4% in the sunlight, is used and therefore, itis low efficiency.

To widen the available range of the light by using a dye to the visiblelight region having the wavelength longer than that of the ultravioletlight, a dye-sensitized solar cell using a ruthenium complex dye isknown as a Gratzel cell. The Gratzel cell has theoretically utilizationefficiency of 30%, practically 10% at the most.

The ruthenium complex dye material is disadvantageous not only in thatit is expensive, but also in that the dye decomposes during the use fora long term and that means a limitation of the lifetime.

Other dyes, particularly various types of organic dyes can be also used,but the organic dyes also have a limitation of the lifetime.

An object of the invention according to the present application is toprovide a photoelectrode material and a solar cell material, which solvethe problems accompanying the photoelectrode and solar cell usingtitanium oxide, and which are inexpensive and require no rutheniumcomplex dye material that is expensive and has a problem about thelifetime.

The present inventors have found that synthetic quartz and fused quartzfunction to generate an electric power as a photovoltaic material whenincorporated in a photocell or photoelectrode.

The present inventors have found that the synthetic quartz and fusedquartz each treated with the halogen acid function to generate anelectric power as a photovoltaic material when incorporated in aphotocell or photoelectrode.

Further, the present inventors have found that the synthetic quartz andfused quartz each treated with the halogen acid function as a photocellmaterial.

In addition, they have found that other glass including silicon oxide(SiO₂), i.e., soda-lime glass, non-alkali glass, and borosilicate glassalso function as a photoelectrode material or a photocell material.

In the invention according to the present application, a materialobtained by treating a silicon oxide composition with the halogen acidis used as a photoelectrode material or a photocell material.

The composition including silicon oxide used in the material issynthetic quartz.

The composition including silicon oxide used in the material is fusedquartz glass.

The composition including silicon oxide used in the material issoda-lime glass.

The composition including silicon oxide used in the material isnon-alkali glass.

The composition including silicon oxide used in the material isborosilicate glass.

The halogen acid used in the halogen acid treatment is hydrofluoricacid. The halogen acid used in the halogen acid treatment ishydrochloric acid.

The use of the material is a photoelectrode. The use of the material isa photocell.

In further aspect of the invention according to the present invention, amethod of generating electricity utilizing the photocell described aboveis provided. The method includes irradiating a light to a photocellcomprising a photovoltaic material which consists essentially of siliconoxide in a manner that causes the silicon oxide to generate theelectricity in response to the irradiation of light, and correcting theelectricity from the photovoltaic material. In one embodiment, themethod of generating electricity includes irradiating a light to aphotocell which comprises a first photovoltaic material comprisingsilicon oxide and a second photovoltaic material other than the silicondioxide in a manner that causes the first and second photovoltaicmaterials to generate the electricity in response to the irradiation oflight, and collecting the electricity from the first and secondphotovoltaic materials.

In one embodiment of the electricity generation method, the irradiatingstep may include irradiating an indoor light which does not include anultraviolet light or may include irradiating a light having a wavelengthlarger than a wavelength of an ultraviolet light.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an arrangement in principle of a water photo electrolysisapparatus using the photoelectrode material according to the presentinvention.

FIG. 2 shows an arrangement in principle of a photocell using thephotocell material according to the present invention.

FIG. 3 shows the specific arrangement of the photocell.

DESCRIPTIONS OF THE INVENTION

The compositions of the materials used in the embodiments and thetreatment therefor are as follows:

(1) synthetic quartz: Crystalline SiO₂(2) Fused quartz glass: Amorphous SiO₂(3) Soda-lime glass: SiO₂: 71.9%, CaO: 7.8%, Al₂O₃: 1.7%, MgO: 4.0%,Na₂O: 13.3%(4) Non-alkali glass: SiO₂: 55.0%, CaO: 23.0%, Al₂O₃: 14.2%, B₂O₃: 6.2%(5) Borosilicate glass: SiO₂: 33.0%, CaO: 6.8%, Al₂O₃: 1.3%, B₂O₃:37.4%, MgO: 5.5%, Na₂O: 16.0%.

The description of the components having a content of less than 1% isomitted.

The above glass sample is immersed in an aqueous solution ofhydrofluoric acid, and washed with water and then dried, and pulverized.

Other than hydrofluoric acid, hydrochloric acid is used as the halogenacid, but hydrofluoric acid is preferred.

Other halogen acids are considered to be able to be used.

It has been confirmed that a glass sample which is not treated with thehalogen acid also functions as a photoelectrode material.

A fluorescent light is used as an indoor light source, and theilluminance obtained in that case is 15,000 to 19,000 lux.

With respect to an outdoor light, the illuminance of 6,000 to 7,000 luxcan be obtained in the shade, and the illuminance of about 50,000 to100,000 lux can be obtained from the sunlight.

Embodiment 1

An example of the photoelectrode is first described.

An apparatus utilizing the photoelectrode ability of the halogenationtreated glass is described with reference to FIG. 1.

In FIG. 1, the reference numeral 1 represents an anode; 2 aphotoelectrode material supported by the anode 1; 3 a cathode; 4 watermixed therein an appropriate electrolyte; and 5 a load connected betweenthe anode 1 and the cathode 3.

The anode 1 is formed from Ni/NiO or a noble metal, and supports thereonthe photoelectrode material 2. The size of the anode is 20 mm×20 mm.

The above glass sample is immersed in the 5% aqueous solution ofhydrofluoric acid for 5 minutes, and washed with water and then dried,and pulverized so that the diameter of the resultant particles becomes0.2 mm or less.

As the cathode 3, for example, platinum or carbon is used.

As the load 5, a resistor is used.

When the photoelectrode material 2 is irradiated with a light at 200 to800 nm wavelength and the light is absorbed by the photoelectrodematerial, charge separation occurs in the photoelectrode material, andthe resultant state has a certain lifetime, so that electrons react withand reduce water to form H₂ and positive holes oxidize water to form O₂.

Thus hydrogen and oxygen are generated and simultaneously, electronsflow from the cathode 3 toward the anode 1 through the load 5, namely, acurrent flows from the anode 1 toward the cathode 3.

Using the electrode 1 having an area of 20×20 mm² and a 0.5 mol/Lelectrolytic solution obtained by dissolving 0.71 g of Na₂SO₄ in 10 mLof pure water, a current flowing when irradiated with a light at 15,000to 19,000 lux using a fluorescent light is shown in Table 1.

Further, the amount of the hydrogen gas generated by electrolysis ofwater, which is determined by making a calculation from theabove-obtained current value, is also shown.

TABLE 1 photoelectrode current hydrogen gas materials (μA) (μL)synthetic quartz 0.2 0.84 fused quartz glass 0.1 0.42 soda-lime glass0.1 0.42 non-alkali glass 0.1 0.42 borosilicate glass 0.1 0.42

Embodiment 2

Using hydrochloric acid as the halogen acid treatment and an aqueoussolution of sodium sulfate as an electrolytic solution, a syntheticquartz electrode causes a current of 0.1 μA to flow.

From a calculation, the amount of hydrogen obtained by electrolysis atthe above current is 0.42 μL per hour.

Embodiment 3

Next, an example of the photocell is described.

FIG. 2 shows a schematic view of the photocell arrangement according tothe invention.

In FIG. 2, the reference numeral 11 represents an electrode; 13 acounter electrode; 12 a photoelectrode supported by the electrode 11; 14an electrolytic solution; and 15 a load connected between the electrode11 and the counter electrode 13.

The electrode 11 is formed from Ni/NiO or a noble metal, and supportsthereon the photoelectrode material 12 comprising SiO₂.

There is used a photoelectrode obtained by immersing grains of glasscomprising SiO₂ or the like in a 5% aqueous solution of hydrofluoricacid for 5 minutes and washing them with water and then drying them, andpulverizing them so that the diameter of the resultant particles becomes0.2 mm or less.

As the counter electrode 13, for example, platinum or carbon is used,and, as the load 15, a resistor is used.

When the photoelectrode 12 is irradiated with the light having thewavelength of 200 to 800 nm and the light is absorbed by thephotoelectrode, electricity is generated in the photoelectrode 12 andelectrons flow from the electrode 11 toward the counter electrode 13through the load 15. Namely, a current flows from the counter electrode13 towards the electrode 11.

Embodiment 4

Next, a specific arrangement of the photocell is described.

FIG. 3 shows a schematic view of the photocell according to the presentinvention.

In FIG. 3, the reference numerals 21 and 23 represent 30 mm×30 mm glasssubstrates having, respectively, an FTO (fluorine-doped tin oxide) layer22 and an FTO layer 24, and the FTO layer 22 and the FTO layer 24function as a charge extraction electrode. An n-type semiconductor layerof zinc oxide (ZnO), titanium oxide (TiO₂) or the like, is formed on theFTO layer where the light enters.

A 20 mm×20 mm platinum film 26 is formed on the FTO layer 24 opposite tothe FTO where the light enters.

A photocell material 27 having the thickness of 0.15 to 0.20 mm, whereglass comprising SiO₂ and an organic electrolyte are mixed, is enclosedbetween the n-type semiconductor layer 25 and the platinum film 26.

The organic electrolyte by adding 0.1 mol of LiI, 0.05 mol of I₂, 0.5mol of 4-tert-butylpyridine, and 0.5 mol of tetrabutylammonium iodide to0.5 mol acetonitrile solvent is used.

An extraction line is attached to the FTO layer 22 and FTO layer 24,which are extraction electrodes for the photocell, thus prepared, andthe extraction electrode 22 side is irradiated with the light of theilluminance of 15,000 to 19,000 lux using a fluorescent light as a lightsource, and an open-circuit voltage and a short-circuit current betweenthe extraction electrodes 22 and 24 were measured.

The open-circuit voltage and short-circuit current obtained as a resultare shown in Table 2.

TABLE 2 photoelectric open-circuit voltage short-circuit currentmaterials (mV) (μA) synthetic quartz 35 0.5 fused quartz glass 30 0.5soda-lime glass 15 0.3 non-alkali glass 30 0.4 borosilicate glass 14 0.3

Embodiment 5

On the silicon oxide composition which is not treated with hydrofluoricacid, the open-circuit voltage and the short-circuit current shown inTable 3 are obtained.

TABLE 3 photoelectric open-circuit voltage short-circuit currentmaterials (mV) (μA) synthetic quartz 3 0.1 fused quartz glass 3 0.2soda-lime glass 5 0.1 non-alkali glass 5 0.1 borosilicate glass 12 0.2

On the glass fiber treated with hydrofluoric acid at the concentrationof 0.1%, the voltage of 26 mV is detected.

From the above results, it has been found that SiO₂ has a function of aphotocell and the SiO, treated with hydrofluoric acid exhibits aremarkably increased photovoltaic voltage.

Further, on the borosilicate glass, a voltage as high as 12 mV isdetected even when it is not treated with hydrofluoric acid, and it isconsidered that such the high voltage may be caused due to the presenceof boric acid (B₂O₃).

Embodiment 6

When using hydrochloric acid instead of halogen acid for the treatmentand the organic electrolyte by adding 0.1 mol of LiI, 0.05 mol of I₂,0.5 mol of 4-tert-butylpyridine, and 0.5 mol of tetrabutylammoniumiodide to acetonitrile solvent, the obtained open-circuit voltage is 4mV, and the obtained short-circuit current is 0.1 μA.

Embodiment 7

With respect to the synthetic quartz, it is measured at the illuminancesubstantially equivalent to that of sunlight using an incandescent lampat 300 W, which is a light source containing no component of anultraviolet region. As a result, the open-circuit voltage of 400 mV andthe short-circuit current of 0.5 μA are obtained.

This result has confirmed that at least the synthetic quartz enables aphotovoltaic action using the light having the wavelength longer thanthat of the ultraviolet light and the resultant electromotive force isnot caused by titanium oxide.

Therefore, even higher open-circuit voltage and larger short-circuitcurrent are expected when further adding a titanium oxide film which hasconventionally been studied for a solar cell.

REFERENCE NUMERALS

-   1, 11: Electrode-   2, 12: Photoelectrode material-   3, 13: Counter electrode-   4, 14: Electrolyte-   5, 15: Load-   21, 23: Glass substrate-   22, 24: Extraction electrode-   25: n-Type semiconductor layer-   26: Platinum film-   27: Silicon oxide

1. A method of generating electricity, comprising: irradiating a lightto a photocell comprising a photovoltaic material which consistsessentially of silicon oxide in a manner that causes the silicon oxideto generate the electricity in response to the irradiation of light; andcorrecting the electricity from the photovoltaic material.
 2. The methodaccording to claim 1, wherein the silicon oxide has been treated withhalogen acid.
 3. The method according to claim 2, wherein the halogenacid is hydrofluoric acid or hydrochloric acid.
 4. The method accordingto claim 1, wherein the silicon oxide is synthetic quartz.
 5. The methodaccording to claim 1, wherein the silicon oxide is fused quartz glass.6. The method according to claim 1, wherein the silicon oxide issoda-lime glass.
 7. The method according to claim 1, wherein the siliconoxide is non-alkali glass.
 8. The method according to claim 1, whereinthe silicon oxide is borosilicate glass.
 9. The method according toclaim 1, wherein the silicon oxide is glass fiber.
 10. The methodaccording to claim 1, wherein said irradiating the light comprisesirradiating an indoor light which does not include an ultraviolet light.11. The method according to claim 1, wherein said irradiating the lightcomprises irradiating a light having a wavelength larger than awavelength of an ultraviolet light.
 12. A method of generatingelectricity, comprising: irradiating a light to a photocell whichcomprises a first photovoltaic material comprising silicon oxide and asecond photovoltaic material other than the silicon dioxide in a mannerthat causes the first and second photovoltaic materials to generate theelectricity in response to the irradiation of light; and collecting theelectricity from the first and second photovoltaic materials.
 13. Themethod according to claim 12, wherein the second photovoltaic materialis titanium oxide.
 14. The method according to claim 12, wherein thesilicon oxide is has been treated with halogen acid.
 15. The methodaccording to claim 14, wherein the halogen acid is hydrofluoric acid orhydrochloric acid.
 16. The method according to claim 12, wherein thesilicon oxide is synthetic quartz or fused quartz glass.
 17. The methodaccording to claim 12, wherein the silicon oxide is selected from thegroup consisting of soda-lime glass, non-alkali glass, and borosilicateglass.
 18. The method according to claim 12, wherein the silicon oxideis glass fiber.
 19. The method according to claim 1, wherein saidirradiating the light comprises irradiating an indoor light which doesnot include an ultraviolet light.
 20. The method according to claim 1,wherein said irradiating the light comprises irradiating a light havinga wavelength larger than a wavelength of an ultraviolet light.